CNH: Competing Demands and Future Vulnerability of Groundwater: Drinking Water Quality and Food Security in Arsenic-Impacted South and Southeast Asia

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Hundreds of millions of people worldwide are exposed to dangerous arsenic (As) levels by drinking untreated groundwater. As contamination causes a variety of severe health problems in humans, including several forms of cancer and increased infant mortality Recent field evidence shows how human activities can elevate As concentrations and suggests many more people could be affected in the coming decades. Massive groundwater pumping for the supply of both megacities and rice irrigation could contaminate deep aquifers that currently have low levels of As, by drawing in groundwater that is high in As. Furthermore, irrigation with high-As groundwater markedly reduces the yield of rice crops, threatening food security. The extent of groundwater contamination in affected areas is determined by a combination of individual farmers' practices and the decisions made by large municipalities. In order to study these interactions, the researchers will model how human decisions affect As levels in aquifers across three river basins that have experienced differing degrees of development. The study will identify effective measures to reduce the amounts of As in groundwater and rice crops, leading to safer food and water supplies. Aquifer vulnerability will be assessed by tracking the penetration of the radioisotopes of hydrogen in water and carbon released to the atmosphere between 1950 and 1970 relative to As in groundwater. Several hundred wells distributed along three 30 km transects, some affected by municipal and irrigation pumping and others not, will be sampled for these and additional tracers. These measurements will be combined with modeling of groundwater flow and As transport to determine whether irrigation pumping or municipal pumping poses a more serious threat. Farmer behavior will be assessed through a randomized controlled trial by providing field-kits for measuring As in irrigation water and paddy soil in some villages and not in others. Currently all rice farmers in the study area use some fertilizer to boost yields, but almost no farmer removes the most contaminated topsoil to reduce As before adding fertilizer and increase yields for years to come. The researchers will examine the tradeoff between a short-term gain and a long-term gain where the one-time investment cost is paired with varying patterns of future benefits. The observations are expected to establish that soil removal and lowering of As in irrigation water will increase rice yields and protect deep low-As groundwater for drinking. More broadly, the research is expected to provide evidence for policy makers that scaling up the adoption of simple alternative approaches can protect groundwater aquifers.